Simple logic would suggest that humans arose from the place with the highest density of current population. Like China or India. Folks have been there longest and, notwithstanding catastrophe, in a macro sense, this is where the highest number should be. If mankind were 25 million years old, the population of the Earth would be in the trillions.
In my humble opinion....
Thats not how it works. Human population because it has no predators grows rapidly until it reaches it’s carrying capacity. Carrying capacity is high in a place with lots of food, living space, etc and low in a place like a desert.
You are thinking of exponential growth when population is actually logistical growth.